• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.16 no.6
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• pp.378-384
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• 2023

In this study, we aim to derive the descriptor vector conditions that can simultaneously achieve the efficiency and accuracy of artificial Neural Network Potentials (NNP). The material system selected is silicon, a highly applicable material in various industries. Atomic structure-dependent energy data for training artificial neural networks were generated through density functional theory calculations. Behler-Parrinello type atomic-centered symmetric functions were employed as descriptors, and various length vector NNPs were generated. These NNPs were applied to reproduce the structure and mechanical properties of silicon materials in molecular dynamics simulations. In our findings, the minimum vector length for achieving both learning and computational efficiency while maintaining property reproducibility is approximately 50. It was also observed that, for the same conditions, incorporating more angle-dependent symmetric functions into the descriptor vector, could enhance the accuracy of NNP. Our results can provide guidelines for optimizing the conditions of descriptor vectors to achieve both efficiency and accuracy of NNP, simultaneously.

• Clean Technology
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• v.19 no.2
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• pp.84-89
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• 2013

The running blots between patterns during electroless nickel electroless palladium immersion gold (ENEPIG) surface finish of printed circuit board (PCB) are investigated and a proper solution is presented. Computational chemistry is first employed to understand the process and experiments are then designed to verify the proposed ideas. A $PdCl_2$ activator which has relatively weak chemical bonding to the epoxy resin is introduced to prevent the formation of palladium seeds on the epoxy resin and a couple of operational measures such as increasing HCl concentration and lowering the temperature of Pd activation process are executed to prevent a further hydrolysis of $PdCl_2$ to more stable $Pd(OH)_2$ in aqueous solution. Computational chemistry provides thermodynamic backgrounds for experiments and their results. This combined approach is expected to be very useful in the research of relevant processes.

• Analytical Science and Technology
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• v.18 no.4
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• pp.309-319
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• 2005

The adsorption characteristics of gaseous molecules on the carbonaceous adsorbent have been investigated at various temperature and pressure with different pore sizes using Grand Canonical Monte Carlo (GCMC) simulation method. The geometrical parameters and spectroscopic properties of adsorbates have been computed using density functional theory (DFT). At higher temperatures is the adsorption amount of adsorbates is decreased due to their vaporization. Considering the pore size effect, the adsorption characteristic depends on the adsorbate size, polarity and interaction between adsorbates, etc. At all cases employed in this study, the adsorption amount of adsorbates on the carbonaceous adsorbent is increased in the order $NH_3$ < $H_2S$ < $CH_3SH$, and this result is qualitatively in good agreement with the experimental observation.

• Journal of the Korean Chemical Society
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• v.54 no.4
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• pp.387-394
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• 2010

The theoretical calculations for $B_nH_n$, $B_nH_{n+1}$, $B_nH_{n+2}$ (n = 3-6) have been considered at the B3LYP level of theory with the 6-311G$^*$ basis set. The optimized geometries, harmonic vibrational frequencies, and binding energies are evaluated to elucidate the thermodynamic stability and spectroscopic properties. The harmonic vibrational frequencies for the molecules considered in this study show all real numbers implying true minima and the binding energies are corrected using zero-point vibrational energies (ZPVE). The binding energies and average energies due to increasing of BH monomer are predicted.

• Journal of the Korean Chemical Society
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• v.50 no.4
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• pp.291-297
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• 2006

The equilibrium structures, relative energies and NBO analyses for the possible conformations and transition states which can exist on the internal rotation of CPDFB and CPCFB molecules have been investigated using DFT and ab initio methods with various basis sets. The interaction between bonding orbital ((C1-C3, C2-C3)) and antibonding orbital (n*(B9) and *(B9-Cl11)) was the main characteristic hyperconjugation in both molecules. In addition, the stabilization energy of CPDFB was 6.63kcal/mol and that of CPCFB was 6.97(E-form)/6.79(Z-form) kcal/mol for each conformation. The rotational barriers by internal rotation of BF2- and BFCl- functional groups were evaluated to be 5.3~6.7kcal/mol and 5.7~6.5kcal/mol respectively, which showed good agreement with the experimental values reported by previous dynamic NMR study. Finally, Z-form was more stable than E-form by 0.2 kcal/mol in CPCFB molecule and therefore Z-form was confirmed as global minimum.

• Journal of the Korean Chemical Society
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• v.55 no.6
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• pp.905-911
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• 2011

The possible minimum structures of $C_{60}(CH_2)_nOH$ (n=0~2) and $C_{60}(OH)_2$have been optimized using density functional theory (DFT) with the 6-311G (d,f) basis set. The harmonic vibrational frequencies and IR intensities are also determined to confirm that all the optimized geometries are true minima. Also zero-point vibrational energies (ZPVE) have been considered to predict the binding energies. The predicted binding energy of $C_{60}CH_2OH$ is about 10 kcal/mol more stable than the binding energy of $C_{60}OH$.

• Journal of the Korean Chemical Society
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• v.60 no.4
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• pp.239-244
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• 2016

We investigated the structures and electronic properties of Cu_mSiO_m+1 clusters with m = 0 - 7. For these clusters, we replaced a Cu atom in the copper oxide clusters with a Si atom. The B3LYP functional and LANL2DZ basis set were used for optimization of the molecular structures of all neutral and charged clusters. The bond distances, bond angles, and Mulliken charges were calculated to study the structural properties. In addition, in order to understand the electronic properties, we examined the ionization energies, electronic affinities, and second differences in energies.

• Journal of the Korean Magnetics Society
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• v.1 no.2
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• pp.9-14
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• 1991

In order to investigate electronic and magnetic properties of $Fe_{16}N_{2}$ ferromagnet, we have performed electronic structure calculations employing the self-consistent local density functional LMTO(linearized muffin tin orbital) band method. We have obtained the ground state parameters, such as band structures, density of states, Stoner parameters, and magnetic moments. Based on these results, we have investigated microscopically the magnetic structure and the enhancement of Fe magnetic moments in this compound. Magnetic moments of 3 types of Fe(Fe I, Fe II and Fe III) in $Fe_{16}N_{2}$ are 2.13, 2.50, and $2.85\;{\mu}_{B}$, respectively. Large enhancement of Fe magnetic moment is observed in Fe II and Fe III, which are located rather far from N. This implies that local environment is very important in determining the Fe magnetic moments in this compound. Our value of average magnetic moment per Fe atom. $2.50\;{\mu}_{B}$, is a bit smaller than the reported estimate, $-3.0\;{\mu}_{B}$, from the experiment.

• Journal of the Korean Geotechnical Society
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• v.23 no.11
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• pp.59-66
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• 2007

In order to clarify the influence of gravel content on the mechanical properties of gravel-mixed decompose granite soils, large-scale one-dimensional compression tests were performed. The sample used in the study was a decomposed granite soil from Shimonoseki in Yamaguchi prefecture in Japan. After adjusting the grain size of the said soils, the specimen compacted with a certain level of compaction energy was put to the test. Based on the results obtained, when gravel-mixed decomposed granite soil was compacted at the same energy level, there existed the specific gravel content at which dry density was maximum and which also produced the minimum compression index. Furthermore, from these results, an expression based on a two-phase mixture theory was proposed to quantitatively evaluate the effects of gravel content and initial dry density and the material parameters calculated through the proposed method proved to exactly estimate the actual measuring value.

• Nuclear Engineering and Technology
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• v.6 no.4
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• pp.253-259
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• 1974

The output signal voltage of the pulsed ionization chamber (PIC) was measured for a range of electron density (10$^{13}$ -10$^{17}$ m$^{-3}$ ) of the 3He plasmas. This experimental data was in excellent agreement with the theory including space charge effects. As an application of the PIC techniques, two-body recombination coefficients were obtained with electron densities measured from output signal voltage of the PIC. These values as a function of pressure were in good agreement with theoretical predictions and ranged from 5$\times$10$^{-14}$ to 3$\times$10$^{-13}$ (㎥/sec) at 300$^{\circ}$K for 1 to 10 atmospheric $^3$He plasma.